Add option to include dotfiles

I love this plugin and only have one issue with it. I can't get it to copy my dotfiles, like `.nojekyll`.

My config:
````
'gh-pages': {
	options: {
		base: 'dist'
	},
	src: ['**']
}
````

I've tried `['**/*']` and `['**/*.*']`. The only way it works is to manually add the file `['**', '.nojekyll']`.

I'd expect all files, including dotfiles, to be included.